A hot melt adhesive is a solvent-less adhesive, which is heat-melted, applied to an adherend, and then solidified by cooling to exhibit adhesion, and thus a hot melt adhesive enables instantaneous adhesion and rapid adhesion, and is applicable in wide variety fields such as paper processing, woodworking, hygienic materials, and electronics.
In recent years, because of an increase in awareness of environmental problems, the replacement of conventional petroleum-derived raw materials by natural materials, plant materials and biodegradable materials has proceeded. In terms of environmental problems, such as global warming due to an increase of carbon dioxide emission, attempts have been made to produce hot melt adhesives using non-petroleum-based resins, such as polylactic acid-based resins, containing no petroleum as a raw material.
Patent document 1 discloses a hot melt adhesive comprising a polylactic acid-based resin, and poly(butylene succinate) or poly(ethylene succinate). Patent document 2 discloses a hot melt adhesive comprising polylactic acid and a polyvinyl alcohol-based resin. Patent document 3 discloses a hot melt adhesive composition that is a composition comprising a thermoplastic resin and a tackifier as main components, wherein either one or both of them comprise a lactic acid copolymer resin derived from polylactic acid or lactic acid and other hydroxycarboxylic acids.
Any of the polylactic acid-based hot melt adhesives in Patent Documents 1 to 3 is suitable for application to paper. The hot melt adhesive in Patent Document 1 is for bookbinding (paragraph number “0001”), and the hot melt adhesive in Patent Document 2 is suitable for packaging paper, packaging container, and corrugated cardboards etc. (paragraph number “0035”). Regarding the hot melt adhesive in Patent Document 3, the adhesion property to corrugated cardboard material is evaluated as shown in a table in Examples.
Meanwhile, a polyolefin-based hot melt adhesive is known as another paper adhesive.
A polylactic acid-based hot melt adhesive tends to be inferior to a polyolefin-based hot melt adhesive in tackiness, adhesion property, and thermal stability, and in particular, has poor adhesion property to a polyolefin substrate for use as a vehicle interior material. Consequently, the polylactic acid-based hot melt adhesives described in Patent Documents 1 to 3 are not be suitably applied to the use for a vehicle interior material.
Blending a polyolefin in a polylactic acid-based hot melt adhesive may be thought as means for enhancing adhesion property to a polyolefin-based substrate. A polylactic acid, however, has problems that it is not easily mixed with a polyolefin, and has poor compatibility with a “tackifier resin” as an additive to a hot melt adhesive, with poor thermal stability.
Patent document 1: Japanese Patent Laid-Open No. 2010-155951
Patent document 2: Japanese Patent Laid-Open No. 2004-256642
Patent document 3: Japanese Patent Laid-Open No. H05 (1993)-339557